1. Field of the Invention
The present invention relates to polymeric compounds which increase, in a liquid crystal display element comprising a liquid crystal layer having a polymer wall and a liquid crystal region substantially surrounded by said polymer wall, the orientation restricting force of a liquid crystal material present in said liquid crystal regions in an interface between said liquid crystal material and said polymer wall, and also relates to a liquid crystal display element using the polymeric compound. The liquid crystal display element of this invention can be utilized for personal display devices such as word processors, personal computers, and the like. The liquid crystal display element can also be utilized in devices used by a number of people such as portable information end devices, and the like.
2. Description of the Related Art
Liquid crystal display elements using a liquid crystal material and a polymer material PA0 The principal behind the improvement of the viewing angle characteristics of a liquid crystal display element PA0 Specific examples of the elements having a wide viewing angle mode
(1) Japanese Laid-open National Patent Publication No. 58-501631 discloses a polymer dispersed liquid crystal display element which comprises a polymer material and a liquid crystal material encapsulated by the polymer material which displays the scattering state of an incident light by the refractive index difference between the liquid crystal material and the polymer material, and also displays the transparent state by the variation of the refractive index of the liquid crystal material with the impression of an electric voltage.
Japanese Laid-open National Patent Publication No. 61-502128 discloses a liquid crystal display element comprising a liquid crystal layer in which the phases of the liquid crystal material and the cured resin are three-dimensionally separated by irradiating a mixture of the liquid crystal material and the photocurable resin with ultraviolet ray.
These elements are basically liquid crystal display elements which control electrically the scattering-transparency variation of an incident light in the liquid crystal layer.
(2) Japanese Laid-open Patent Publication No. 1-269922 discloses a technique for preparing liquid crystal regions with different characteristics by first exposing to ultraviolet ray a liquid crystal layer comprising a photocurable resin and a liquid crystal material through a photo-mask, and further irradiating it with ultraviolet ray after remove the photo-mask. The element thus obtained is basically a scattering type element.
Japanese Laid-open Patent Publication No. 5-257135 discloses an element comprising a liquid crystal layer obtained by oppositely placing a substrate equipped with an alignment film having an orientation restricting force through a pair of gaps, injecting a mixture of a liquid crystal material and a photocurable resin into the gaps, and then irradiating the mixture with ultraviolet rays through a photo-mask disposed on the surface of said substrate. Since the inner portion of the liquid crystal layer in which the photo-mask is disposed has different threshold values and different optical characteristics obtained from the impression of an electric voltage from those of the outer portion of the liquid crystal layer, the element is a static driving element in which the pixel patterns are varied due to the electric voltage.
In order to improve the viewing angle characteristics of a liquid crystal display element, it is necessary to orient each of the liquid crystal molecule toward three or more different directions inside the pixels (liquid crystal regions). If each of the liquid crystal molecules inside the liquid crystal layer is oriented in three or more different directions, the apparent refractive index of each of the liquid crystal molecules is averaged in the gray scale state when viewing the pixels from both A and B directions as described in FIG. 1B. In other words, the contrast of the display element is substantially identical from both A and B directions. Therefore, the viewing angle characteristics of the element having such an orientation state of the liquid crystal as shown in FIG. 1B are improved, compared to those of the element having a TN mode shown in FIG. 2B.
(1) Japanese Laid-open Patent Publications Nos. 4-338923 and 4-212928 disclose a wide viewing angle mode comprising a combination of the aforementioned polymer dispersed liquid crystal element and polarizing plates, which are attached to both surfaces of the element such that each of the polarization axes of the plates are at a right angle to each other.
(2) As a method for improving the viewing angle characteristics of a non-scattering type liquid crystal display element using a polarizer, Japanese Laid-open Patent Publication No. 5-27242 discloses a method for preparing a composite material of a liquid crystal and a polymer from a mixture of the liquid crystal and a photocurable resin by the phase separation. According to this method, the orientation of the liquid crystal domains becomes random due to the polymer thus prepared. Therefore, because the liquid crystal molecules are oriented in different directions in each domain at the time of impressing an electric voltage, the apparent refractive indices viewed from each direction are substantially identical, and the viewing angle characteristics are improved in the gray scale state.
(3) In recent years, the present inventors have proposed a liquid crystal display element comprising a liquid crystal region in which the liquid crystal molecules are omnidirectionally (spirally) oriented in the portions where a photo-mask is present, and a polymer wall which consists mainly of a photocurable resin in the other portions. The liquid crystal region and polymer wall are formed by irradiating through the photo-mask a cell having a liquid crystal composition comprising the photocurable resin and the liquid crystal material. When the liquid crystal molecules of the liquid crystal display element are controlled by an electric voltage, the spiral orientation of the liquid crystal molecules will act as if an umbrella opened and closed to improve significantly the viewing angle characteristics.
In the interface between the polymer wall and the liquid crystal material of the element described in (3), disclination lines are generated due to the reverse tilt of the liquid crystal molecules at the time of impressing an electric voltage. Since the disclination lines are displayed as bright lines, the viewing angle characteristics of the element are deteriorated, when the display state is in a black state.
The prevent inventors have found that the addition of a polymeric compound to a mixture of the liquid crystal material and the photocurable resin in order to prevents the generation of the disclination lines in these elements. However, because the addition of the conventional polymeric compounds enlarges the pretilt angle of the liquid crystal material in the liquid crystal regions, the brightness of the element is reduced in the absence of an electric voltage.
The present inventors have eagerly examined the relationship between the structure of the polymeric compounds and the orientation of the liquid crystal molecules in the interface between the liquid crystal material and the polymer wall, and found a compound from which a liquid crystal display element is obtained generating no disclination lines and also having bright characteristics in the absence of an electric voltage.